Conventionally, there has been known a technique of drawing (displaying or printing) an image by superimposing a predetermined image (for example, a digital watermark image, a background pattern or the like) on image data of an original image.
For example, Patent Literature 1 discloses the following technique: a plurality of digital watermarks are generated by use of a plurality of keys that differ depending on a feature of a content or elapse of time, and each of the generated plurality of digital watermarks is then embedded in a corresponding signal to be processed. This allows a proper detector to effectively and accurately detect a digital watermark by extracting the feature of the content. Further, this also makes it impossible for a third person who does not know the plurality of keys to detect the digital watermark from the signal in which the digital watermark is embedded.
Patent Literature 1    Japanese Patent Application Publication, Tokukai, No. 2002-320085 A (Publication Date: Oct. 31, 2002)